<template>
    <div class="list">
        <ul class="item-wrapper">
            <li 
                class="item"
                v-for="item of letters"
                :key="item"
                :ref="item"
                @touchstart.prevent="handleTouchStart"
                @touchmove="handleTouchMove"
                @touchend="handleTouchEnd"
                @click="handleLetterClick"
            >
            {{item}}
            </li>
        </ul>
    </div>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
   .item-wrapper
        display: flex
        flex-direction: column
        justify-content: center
        position: absolute
        right: 0
        top: 1.58rem
        bottom: 0
        width: .4rem
        .item
            text-align: center
            line-height: .4rem
            color: $bgColor
</style>
